1. Field of the Invention
This invention relates to a retractable lens barrel wherein a movable barrel is protrudable from a fixed barrel or a camera body. More particularly, the invention provides a new lens barrel which can be made compact even when it contains movable lenses of a variable power system and/or a focusing system; the length of which in the front-rear (axial) direction can be reduced; the number of parts reduced; and the optical axes of different lens groups and an iris unit of which do not readily become misaligned when the lens barrel case is being assembled.
2. Description of the Prior Art
Retractable-type lens barrels wherein a movable barrel is protrudable from a fixed barrel or a camera body to improve the portability of the camera are known.
FIG. 1 and FIG. 2 are schematic views of an example of such a known lens barrel which is retractable into a camera body.
Referring to FIG. 1 and FIG. 2, a lens barrel 1a is mounted movably in its optical axis direction with respect to a camera body 1b; during filming, the lens barrel 1a projects forward from the camera body 1b and is in a filming-possible state (see FIG. 1). When the camera is not being used the lens barrel 1a is retracted into the camera body 1b and is in a filming-impossible state (see FIG. 2).
A zoom lens 1c is mounted in a lens holder 1d and the lens holder 1d is mounted movably with respect to the lens barrel 1a; the zoom lens 1c is moved inside the camera body 1b in the optical axis direction and zooming is thereby effected by a drive mechanism not shown in the drawings.
By the lens barrel 1a being contracted, most of the lens barrel 1a can be received into the camera body 1b and the whole camera when not in use can be made compact.
However, in the lens barrel 1a described above, because the zoom lens 1c is mounted inside the lens barrel 1a movably with respect thereto, a space le for this lens barrel 1a to be retracted into must be provided inside the camera body 1b, and there has been the problem that the size of the whole camera consequently becomes large.
The space 1e formed inside the camera body 1b for the lens barrel 1a to be retracted into becomes wasted space when the lens barrel 1a has been protruded, and because besides this space 1e a space 1f for a focusing lens and an iris mechanism and the like to be disposed in is necessary in the camera body 1b, the size of the camera body 1b in the optical axis direction has been large.
Also, for example in the design of a lens barrel of a high variable power rate, it is necessary for the range of movement of the zoom lens 1c to be made large, and in this case the space 1e in which the zoom lens 1c can move in the camera body 1b must be made large, the lens barrel 1a itself must be made large in the optical axis direction, and when the large lens barrel 1a is all to be retracted into the camera body 1b, the camera body 1b has had to be made large.
FIG. 3 and FIG. 4 on the other hand, show an example of a conventional camera lens barrel 2a wherein a case 2b comprises a cylindrical front half 2c and a cylindrical rear half 2d slightly smaller than the front half 2c joined together one in front of the other (the left side of FIG. 5 will be taken as the front and the right side as the rear).
A first lens group 2e is a positive lens group, a second lens group 2f is a negative lens group, a third lens group 2g is a positive lens group and a fourth lens group 2h is also a positive lens group.
The four lens groups 2e, 2f, 2g and 2h are arrayed in the above order on a common optical axis x--x extending in the front-rear direction through the center of the case 2b as seen in the front-rear direction.
An iris unit 2i comprising a casing 2j containing diaphragm vanes 2k, 2k for light quantity control is mounted on the rear end of the front half 2c of the case 2b.
The first lens group 2e is fixed by suitable means to the front end of the front half 2c of the case 2b and the front of the case 2b is thereby closed off.
A slidable lens holder 21 is slidably mounted on slide shafts 2m, 2m mounted on the upper and lower sides of the front half 2c of the case 2b, and the second lens group 2f is mounted in the slidable lens holder 21 and constitutes a zooming lens.
A fixed lens holder 2n holding the third lens group 2g is mounted by suitable means on the rear surface of the casing 2j of the iris unit 2i.
A sliding lens holder 2o is slidably mounted on slide shafts 2p, 2p mounted on the upper and lower sides of the rear half 2d of the case 2b, and the fourth lens group 2h is mounted in the sliding lens holder 2o and constitutes a focusing lens.
A low pass filter 2q is mounted behind the fourth lens group 2h.
The double-dot broken line 2r in FIG. 4 indicates the diaphragm central position of the diaphragm vanes 2k, 2k, and this line serves as a reference for setting the distance between the diaphragm and the third lens group 2g.
With the conventional camera lens barrel 2a, because making the four lens groups 2e, 2f, 2g and 2h thinner than they are at present is very difficult due to problems of refraction and the like, and because it is not possible to make the movement spaces of the second lens group 2f and the fourth group 2h smaller, it has not been possible to shorten the front-rear direction length of the case 2b.
Also, because the case 2b is made by joining together four parts comprising the front half 2c, the iris unit 2i, the fixed lens holder 2n and the rear half 2d, when even slight deviations occur during assembly, these slight deviations add up to a large deviation. Thus, it has been extremely difficult to align the optical axes of the four lens groups 2e, 2f, 2g and 2h and the center of the iris unit 2i on the optical axis x--x.
There has also been the problem that even when the fixed lens holder 2n and the iris unit 2i are made in conformity with their design, if deviation arises when the fixed lens holder 2n is mounted on the rear surface of the casing 2j of the iris unit 2i, the distance between the diaphragm center position 2r of the diaphragm vanes 2k, 2k and the third lens group 2g becomes incorrect.